The relation between shift and ballistic currents in the theory of photogalvanic effect

Abstract

For phototransitions between nondegenerate bands the shift contribution to current, related to the density matrix elements that are nondiagonal regarding the numbers of bands, is compared with the contributions of common nature, conforming to asymmetry of carrier velocity distribution. It is shown that the shift recombination contribution to current, directed along the polar axis can prevail on the absorption edge of ferroelectric crystals. The shift and ballistic phonon contributions in piezoelectrics are comparable in magnitude and can partially compensate for each other. The character of the compensation depends on the type of optical transition and on the form of electron-phonon interaction.